1. PA uses Vala's "Posix" package (see line 23 of libpulse.vapi).
These dependencies have to be declared in the *.deps file.
2. Fix obvious copy/paste error.
3. Rename the parameter to match the C function. This simplifies
understanding what this parameter means.
4. According to the official documentation the "dev" parameter
for playback/capture streams on connection may be NULL and this
is the default. Change the method definition accordingly.